Atomic theory  gr 9
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Atomic theory gr 9

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Notes on Atomic theory 1800 -1913, May 24

Notes on Atomic theory 1800 -1913, May 24

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    Atomic theory  gr 9 Atomic theory gr 9 Presentation Transcript

    • ATOMIC THEORY Lewis
    • 1700’s
      • • In the 1700’s scientist agreed that elements could not be broken down.
      • • 30 +/- elements identified or known
      • • Belief that elements could be mixed together to form compounds
    • 1808 - John Dalton
      • • Dalton proposed an Atomic Theory
      • to explain chemical reactions.
      • • He envisioned the ATOM .
      • * smallest particles of an element
      • * smooth solid sphere
      • * no electrical charge
      • • there was a belief that atoms and molecules were thought to be the same until Dalton.
      • • Scientists now believed that 2 or more
      • Non-Metalic atoms could be combined to form compounds.
    • 1808 - John Dalton Theory
      • • All matter was made of ATOMS - these were to small to see.
      • • Each element has its own kind of Atom with its own mass.
      • • All Atoms of a single type of element are identical.
      • • Compounds are created when atoms of different elements combine in a specific ratio.
      • • Atoms can not be created, destroyed, or subdivided during a chemical change
    • In the 1800’s
      • • until Dalton’s work many scientists believed that molecules and atoms were the same.
      • • after Dalton it was accepted that a molecule was the combination of two or more non-metal atoms in combination.
      • • in 1830 Michael Faraday showed atoms
      • can gain electrical charges.
      • (static electricity)
    • Michael Faraday
      • added the following to ATOMIC THEORY
      • • matter must contain positive (+) and negative (-) charges.
      • • opposite charges attract & like repel
      • • atoms combine to form the particles of a compound because of the electrical attraction between the charges atoms ( Ions ).
    • 1898 - J.J. Thomson
      • • discovered the presence of smaller particles than the atom… the negatively charged ELECTRON,
      • • he proposed than the atom is mostly positively charged matter with small negatively charged electrons scattered randomly throughout.
      • The Plum Pudding Model
      • ( or the chocolate cookie )
    • Thomson’s revisions to Atomic theory
      • • Atoms contain electrons.
      • • electrons have a negative charge and a very small mass.
      • • the rest of the Atom is positively charged.
      • • electrons can be added and removed.
      • ( ie. Rubbing a balloon against cloth )
    • Ernest Rutherford - 1911 the Canadian connection
      • While at the University of McGill, Quebec, Rutherford shot alpha particles at gold foil and found that most went straight through.
      • He reasoned that most of the mass and the positive particles were at the centre of the atom… he called this the nucleus.
    • Ernest Rutherford Rutherford amended the Atomic Theory to include the following.
      • • the Nucleus contains all of the positive charges and most of the mass.
      • • the Nucleus contains positively charged Protons and uncharged Neutrons.
      • • Neutrons have some mass, Protons have more.
      • • the Nucleus is very small.
      • • Electrons orbit the nucleus like satellites.
      • • the mass of an electron is 1/1800 of the protons.
      • • the size of an atom is determined by the size of orbit of electrons.
      • • there is empty space between the nucleus and the electrons.
      • • When Rutherford published his findings in 1912, he knew that his version of the ATOMIC THEORY already had errors and would need to be revised.
      Modern Atomic Theory
    •